Method of transmitting control information in wireless communication system

ABSTRACT

A method of transmitting control information in a wireless communication system is provided. The method includes configuring downlink control information including a plurality of information fields according to a format of scheduling for transmission of a single codeword in a spatial multiplexing mode, wherein the plurality of information fields include a precoding matrix indicator (PMI) confirmation filed for indicating whether precoding is performed on downlink data by using a PMI reported by a user equipment and a transmitted precoding matrix indicator (TPMI) information field for indicating a codebook index, and at least one of the PMI confirmation field and the TPMI information field indicates an offset value of power for the downlink data transmission or interference information for the downlink data transmission, and transmitting the downlink control information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/092,071, filed on Aug. 27, 2008, and claims thebenefit of earlier filing date and right of priority to Korean PatentApplication No. 10-2009-0042820 filed on May 15, 2009, the contents ofall of which are hereby incorporated by reference herein in theirentireties.

BACKGROUND

1. Technical Field

The present invention relates to wireless communications, and moreparticularly, to a method of transmitting downlink control information.

2. Related Art

Recently, to maximize performance and communication capability of awireless communication system, a multiple input multiple output (MIMO)system has drawn attention. Being evolved from the conventionaltechnique in which a single transmit (Tx) antenna and a single receive(Rx) antenna are used, a MIMO technique uses multiple Tx antennas andmultiple Rx antennas to improve transfer efficiency of data to betransmitted or received. The MIMO system is also referred to as amultiple antenna system. In the MIMO technique, instead of receiving onewhole message through a single antenna path, data segments are receivedthrough a plurality of antennas and are then collected as one piece ofdata. As a result, a data transfer rate can be improved in a specificrange, or a system range can be increased with respect to a specificdata transfer rate.

The MIMO technique includes transmit diversity, spatial multiplexing,and beamforming. The transmit diversity is a technique in which themultiple Tx antennas transmit the same data so that transmissionreliability increases.

The spatial multiplexing is a technique in which the multiple Txantennas simultaneously transmit different data so that data can betransmitted at a high speed without increasing a system bandwidth. Thebeamforming is used to add a weight to multiple antennas according to achannel condition so as to increase a signal to interference plus noiseratio (SINR) of a signal. The weight can be expressed by a weight vectoror a weight matrix. The weight vector is referred to as a precedingvector. The weight matrix is referred to as a preceding matrix.

The spatial multiplexing is classified into single-user spatialmultiplexing and multi-user spatial multiplexing.

The single-user spatial multiplexing is also referred to as single userMIMO (SU-MIMO). The multi-user spatial multiplexing is also referred toas spatial division multiple access (SDMA) or multi user MIMO (MU-MIMO).A capacity of a MIMO channel increases in proportion to the number ofantennas. The MIMO channel can be decomposed into independent channels.If the number of Tx antennas is Nt and the number of Rx antennas is Nr,the number of independent channels is Ni where Ni≦min{Nt, Mr}. Eachindependent channel can be referred to as a spatial layer. A rankrepresents the number of non-zero eigenvalues of the MIMO channel andcan be defined as the number of spatial streams that can be multiplexed.

Control information for data transmission is transmitted to a userequipment (UE) through a downlink control channel. Downlink controlinformation includes various types of information required for datatransmission and reception. The UE may transmit data by receivingcontrol information through the downlink control channel. The downlinkcontrol information is configured with several formats according to datato be transmitted. In the MIMO system, the downlink control informationfurther includes preceding information. The preceding information may beunnecessary according to a data transmission mechanism of the MIMOsystem. For example, when using the SU-MIMO, the UE selects a specificfrequency band from a wideband and transmits a preceding matrixindicator (PMI) for the selected frequency band, and when using theMU-MIMO, the UE transmits only a PMI for the wideband. A confirmationmessage is transmitted for the PMI transmitted by the UE, but isunnecessary information when using the MU-MIMO.

Accordingly, there is a need for a method for preventing unnecessaryinformation from being included in downlink control informationaccording to a predetermined format and for effectively transmitting thedownlink control information.

SUMMARY

The present invention provides a method of effectively transmittingdownlink control information.

In an aspect, a method of transmitting control information in a wirelesscommunication system includes configuring downlink control informationincluding a plurality of information fields according to a format ofscheduling for transmission of a single codeword in a spatialmultiplexing mode, wherein the plurality of information fields include apreceding matrix indicator (PMI) confirmation filed for indicatingwhether preceding is performed on downlink data by using a PMI reportedby a user equipment and a transmitted preceding matrix indicator (TPMI)information field for indicating a codebook index, and at least one ofthe PMI confirmation field and the TPMI information field indicates anoffset value of power for the downlink data transmission or interferenceinformation for the downlink data transmission, and transmitting thedownlink control information.

In another aspect, a method of processing data in a wirelesscommunication system includes receiving downlink control informationincluding a plurality of information fields through a downlink controlchannel, and receiving downlink data by using power information orinterference information indicated by the downlink control information,wherein the power information or the interference information istransmitted using a field indicating whether a PMI reported by a userequipment is used in the downlink data transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a structure of a wireless communication system.

FIG. 2 is a block diagram showing functional split between an evolveduniversal terrestrial radio access network (E-UTRAN) and an evolvedpacket core (EPC).

FIG. 3 is a block diagram showing constitutional elements of a userequipment.

FIG. 4 is a diagram showing a radio protocol architecture for a userplane.

FIG. 5 is a diagram showing a radio protocol architecture for a controlplane.

FIG. 6 shows mapping between downlink logical channels and downlinktransport channels.

FIG. 7 shows mapping between downlink transport channels and downlinkphysical channels.

FIG. 8 shows a structure of a radio frame.

FIG. 9 shows an example of a resource grid for one downlink slot.

FIG. 10 shows a structure of a subframe.

FIG. 11 is a flowchart showing a method of configuring a physicaldownlink control channel (PDCCH).

FIG. 12 shows a method of transmitting control information according toan embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 shows a structure of a wireless communication system. Thewireless communication system may have a network structure of anevolved-universal mobile telecommunications system (E-UMTS). The E-UMTSmay be also referred to as a long term evolution (LTE) system. Thewireless communication system can be widely deployed to provide avariety of communication services, such as voices, packet data, etc.

Referring to FIG. 1, an evolved-UMTS terrestrial radio access network(E-UTRAN) includes at least one base station (BS) 20 which provides acontrol plane and a user plane.

A user equipment (UE) 10 may be fixed or mobile, and may be referred toas another terminology, such as a mobile station (MS), a user terminal(UT), a subscriber station (SS), a wireless device, etc. The BS 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as an evolved node-B (eNB), abase transceiver system (BTS), an access point, etc. There are one ormore cells within the coverage of the BS 20. The cell is a region inwhich the BS 20 transmits a communication service. Interfaces fortransmitting user traffic or control traffic may be used between the BSs20. Hereinafter, a downlink is defined as a communication link from theBS 20 to the UE 10, and an uplink is defined as a communication linkfrom the UE 10 to the BS 20.

The BSs 20 are interconnected by means of an X2 interface. The BSs 20are also connected by means of an S1 interface to an evolved packet core(EPC), more specifically, to a mobility management entity (MME)/servinggateway (S-GW) 30. The S1 interface supports a many-to-many relationbetween the BS 20 and the MME/S-GW 30.

The wireless communication system may be an orthogonal frequencydivision multiplexing (OFDM)/orthogonal frequency division multipleaccess (OFDMA)-based system. The OFDM uses a plurality of orthogonalsubcarriers. Further, the OFDM uses an orthogonality between inversefast Fourier transform (IFFT) and fast Fourier transform (FFT). Atransmitter transmits data by performing IFFT. A receiver restoresoriginal data by performing FFT on a received signal. The transmitteruses IFFT to combine the plurality of subcarriers, and the receiver usesFFT to split the plurality of subcarriers.

The wireless communication system may be a multiple antenna system. Themultiple antenna system may be a multiple input multiple output (MIMO)system. The multiple antenna system may be a multiple-inputsingle-output (MISO) system, a single-input single-output (SISO) system,or a single-input multiple-output (SIMO) system. The MIMO system uses aplurality of transmit (Tx) antennas and a plurality of receive (Rx)antennas. The MISO system uses a plurality of Tx antennas and one Rxantenna. The SISO system uses one Tx antenna and one Rx antenna. TheSIMO system uses one Tx antenna and a plurality of Rx antennas.

The multiple antenna system can use a scheme using multiple antennas. Incase of a rank 1, the scheme may be space-time coding (STC) (e.g., spacefrequency block code (SFBC) and space time block code (STBC)), cyclicdelay diversity (CDD), frequency switched transmit diversity (FSTD),time switched transmit diversity (TSTD), etc. In case of a rank 2 orhigher ranks, the scheme may be spatial multiplexing (SM), generalizedcyclic delay diversity (GCDD), selective virtual antenna permutation(S-VAP), etc. The SFBC is a scheme for effectively applying selectivityin a space domain and a frequency domain to ensure both a diversity gainand a multi-user scheduling gain in a corresponding dimension. The STBCis a scheme for applying selectivity in the space domain and a timedomain. The FSTD is a scheme in which signals transmitted to multipleantennas are divided in the time domain, and the TSTD is a scheme inwhich the signals transmitted to the multiple antennas are divided inthe frequency domain. The SM is a scheme for transmitting different datato each antenna to improve a transfer rate. The GCDD is a scheme forapplying selectivity in the time domain and the frequency domain. TheS-VAP is a scheme using a single preceding matrix, and includes amulti-codeword (MCW) S-VAP for mixing multi-codewords to antennas inspatial diversity or spatial multiplexing and a single codeword (SCW)S-VAP using a single codeword.

FIG. 2 is a block diagram showing functional split between the E-UTRANand the EPC. Slashed boxes depict radio protocol layers and white boxesdepict the functional entities of the control plane.

Referring to FIG. 2, the BS performs the following functions: (1)functions for radio resource management (RRM) such as radio bearercontrol, radio admission control, connection mobility control, anddynamic allocation of resources to the UE; (2) Internet protocol (IP)header compression and encryption of user data streams; (3) routing ofuser plane data to the S-GW; (4) scheduling and transmission of pagingmessages; (5) scheduling and transmission of broadcast information; and(6) measurement and measurement reporting configuration for mobility andscheduling.

The MME performs the following functions: (1) non-access stratum (NAS)signaling; (2) NAS signaling security; (3) idle mode UE reachability;(4) tracking area list management; (5) roaming; and (6) authentication.

The S-GW performs the following functions: (1) mobility anchoring; and(2) lawful interception. A PDN gateway (P-GW) performs the followingfunctions: (1) UE IP allocation; and (2) packet filtering.

FIG. 3 is a block diagram showing constitutional elements of the UE. AUE 50 includes a processor 51, a memory 52, a radio frequency (RF) unit53, a display unit 54, and a user interface unit 55. Layers of the radiointerface protocol are implemented in the processor 51. The processor 51provides the control plane and the user plane. The function of eachlayer can be implemented in the processor 51. The memory 52 is coupledto the processor 51 and stores an operating system, applications, andgeneral files. The display unit 54 displays a variety of information ofthe UE 50 and may use a well-known element such as a liquid crystaldisplay (LCD), an organic light emitting diode (OLED), etc. The userinterface unit 55 can be configured with a combination of well-knownuser interfaces such as a keypad, a touch screen, etc. The RF unit 53 iscoupled to the processor 51 and transmits and/or receives radio signals.

Layers of a radio interface protocol between the UE and the network canbe classified into a first layer (L1), a second layer (L2), and a thirdlayer (L3) based on the lower three layers of the open systeminterconnection (OSI) model that is well-known in the communicationsystem. The first layer is a physical (PHY) layer. The second layer canbe divided into a medium access control (MAC) layer, a radio linkcontrol (RLC) layer, and a packet data convergence protocol (PDCP)layer. The third layer is a radio resource control (RRC) layer. The PHYlayer provides an information transfer service through a physicalchannel. The RRC layer belongs to the third layer and serves to controlradio resources between the UE and the network. The UE and the networkexchange RRC messages via the RRC layer.

FIG. 4 is a diagram showing a radio protocol architecture for the userplane. FIG. 5 is a diagram showing a radio protocol architecture for thecontrol plane. They illustrate the architecture of a radio interfaceprotocol between the UE and the E-UTRAN. The user plane is a protocolstack for user data transmission. The control plane is a protocol stackfor control signal transmission.

Referring to FIGS. 4 and 5, between different PHY layers (i.e., a PHYlayer of a transmitter and a PHY layer of a receiver), data istransferred through a physical channel. The PHY layer is coupled with aMAC layer, i.e., an upper layer of the PHY layer, through a transportchannel. Between the MAC layer and the PHY layer, data is transferredthrough the transport channel. The PHY layer provides the MAC layer andan upper layer with an information transfer service through thetransport channel.

The MAC layer provides services to an RLC layer, i.e., an upper layer ofthe MAC layer, through a logical channel. The RLC layer supportsreliable data transmission. The PDCP layer performs a header compressionfunction to reduce a header size of an IP packet.

The RRC layer is defined only in the control plane. The RRC layercontrols radio resources between the UE and the network. For this, inthe RRC layer, RRC messages are exchanged between the UE and thenetwork. The RRC layer serves to control the logical channel, thetransport channel, and the physical channel in association withconfiguration, reconfiguration and release of radio bearers. A radiobearer is a service provided by the second layer for data transmissionbetween the UE and the E-UTRAN. When an RRC connection is establishedbetween an RRC layer of the UE and an RRC layer of the network, it iscalled that the UE is in an RRC connected mode. When the RRC connectionis not established yet, it is called that the UE is in an RRC idle mode.

A non-access stratum (NAS) layer belongs to an upper layer of the RRClayer and serves to perform session management, mobility management, orthe like.

FIG. 6 shows mapping between downlink logical channels and downlinktransport channels. The section 6.1.3.2 of 3GPP TS 36.300 V8.5.0(2008-05) Technical Specification Group Radio Access Network; EvolvedUniversal Terrestrial Radio Access (E-UTRA) and Evolved UniversalTerrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2(Release 8) may be incorporated herein by reference.

Referring to FIG. 6, a paging control channel (PCCH) is mapped to apaging channel (PCH). A broadcast control channel (BCCH) is mapped to abroadcast channel (BCH) or a downlink shared channel (DL-SCH). A commoncontrol channel (CCCH), a dedicated control channel (DCCH), a dedicatedtraffic channel (DTCH), a multicast control channel (MCCH), and amulticast traffic channel (MTCH) are mapped to the DL-SCH. The MCCH andMTCH are also mapped to a multicast channel (MCH).

A type of each logical channel is defined according to a type ofinformation to be transmitted. A logical channel is classified into twogroups, i.e., a control channel and a traffic channel.

The control channel is used for the transfer of control planeinformation. The BCCH is a downlink control channel for broadcastingsystem control information. The PCCH is a downlink channel fortransmitting paging information and is used when a network does not knowthe location of a UE. The CCCH is a channel for transmitting controlinformation between the UE and the network and is used when there is noRRC connection established between the UE and the network. The MCCH is apoint-to-multipoint downlink channel used for transmitting multimediabroadcast multicast service (MBMS) control information. The DCCH is apoint-to-point bi-directional channel for transmitting dedicated controlinformation between the UE and the network, and is used by UEs having anRRC connection.

The traffic channel is used for the transfer of user plane information.The DTCH is a point-to-point channel used for the transfer of userinformation. The DTCH can exist in both uplink and downlink. The MTCH isa point-to-multipoint downlink channel for transmitting traffic data andis used by the UEs that receive the MBMS.

The transport channel is classified according to a type andcharacteristic of data transmission through a radio interface. The BCHis broadcast in the entire coverage area of the cell and has a fixed,pre-defined transport format. The DL-SCH is characterized by support forhybrid automatic repeat request (HARQ), support for dynamic linkadaptation by varying modulation, coding, and Tx power, possibility tobe broadcast in the entire cell, and possibility to use beamforming,support for both dynamic and semi-static resource allocation, supportfor discontinuous reception (DRX) to enable UE power saving, and supportfor MBMS transmission. The PCH is characterized by support for DRX toenable UE power saving and support for broadcast in the entire coveragearea of the cell. The MCH is characterized by support for broadcast inthe entire coverage area of the cell and support for an MBMS singlefrequency network (MBSFN).

FIG. 7 shows mapping between downlink transport channels and downlinkphysical channels.

The section 5.3.1 of 3GPP TS 36.300 V8.5.0 (2008-05) may be incorporatedherein by reference.

Referring to FIG. 7, a BCH is mapped to a physical broadcast channel(PBCH). An MCH is mapped to a physical multicast channel (PMCH). A PCHand a DL-SCH are mapped to a physical downlink shared channel (PDSCH).The PBCH carries a BCH transport block. The PMCH carries the MCH. ThePDSCH carries the DL-SCH and the PCH.

Examples of a downlink physical control channel used in the PHY layerinclude a physical downlink control channel (PDCCH), a physical controlformat indicator channel (PCFICH), a physical hybrid ARQ indicatorchannel (PHICH), etc. The PDCCH informs a UE of resource assignment ofthe PCH and DL-SCH, and also informs the UE of HARQ information relatedto the DL-SCH. The PDCCH may carry an uplink scheduling grant whichinforms the UE of resource assignment for uplink transmission. ThePCFICH informs the UE of the number of OFDM symbols used fortransmission of the PDCCHs within a subframe. The PCFICH can betransmitted in every subframe. The PHICH carries HARQ acknowledgement(ACK)/negative-acknowledgement (NACK) signals in response to uplinktransmission.

FIG. 8 shows a structure of a radio frame.

Referring to FIG. 8, the radio frame consists of 10 subframes. Onesubframe consists of two slots. Slots included in the radio frame arenumbered with slot numbers 0 to 19. A time required to transmit onesubframe is defined as a transmission time interval (TTI). The TTI maybe a scheduling unit for data transmission. For example, one radio framemay have a length of 10 milliseconds (ms), one subframe may have alength of 1 ms, and one slot may have a length of 0.5 ms.

The radio frame of FIG. 8 is shown for exemplary purposes only. Thus,the number of subframes included in the radio frame or the number ofslots included in the subframe or the number of OFDM symbols included inthe slot may change variously.

FIG. 9 shows an example of a resource grid for one downlink slot.

Referring to FIG. 9, the downlink slot includes a plurality of OFDMsymbols in a time domain and N^(DL) resource blocks (RBs) in a frequencydomain. The number N^(DL) of resource blocks included in the downlinkslot depends on a downlink transmission bandwidth determined in a cell.For example, in an LTE system, N^(DL) may be any one value in the rangeof 60 to 110. One RB includes a plurality of subcarriers in thefrequency domain.

Each element on the resource grid is referred to as a resource element.The resource element on the resource grid can be identified by an indexpair (k, l) within the slot. Herein, k (k=0, . . . , N^(DL)×12−1)denotes a subcarrier index in the frequency domain, and l (l=0, . . . ,6) denotes an OFDM symbol index in the time domain.

Although it is described herein that one RB includes 7×12 resourceelements consisting of 7 OFDM symbols in the time domain and 12subcarriers in the frequency domain for example, the number of OFDMsymbols and the number of subcarriers in the RB are not limited thereto.Thus, the number of OFDM symbols and the number of subcarriers maychange variously depending on a cyclic prefix (CP) length, a frequencyspacing, etc. For example, when using a normal CP, the number of OFDMsymbols is 7, and when using an extended CP, the number of OFDM symbolsis 6. In one OFDM symbol, the number of subcarriers may be selected from128, 256, 512, 1024, 1536, and 2048.

FIG. 10 shows a structure of a subframe.

Referring to FIG. 10, the subframe includes two consecutive slots. Amaximum of three OFDM symbols located in a front portion of a 1st slotwithin the subframe correspond to a control region to be assigned with aPDCCH. The remaining OFDM symbols correspond to a data region to beassigned with a PDSCH. In addition to the PDCCH, control channels suchas a PCFICH, a PHICH, etc., can be assigned to the control region. TheUE can read data information transmitted through the PDSCH by decodingcontrol information transmitted through the PDCCH. Although the controlregion includes three OFDM symbols herein, this is for exemplarypurposes only. Thus, two OFDM symbols or one OFDM symbol may be includedin the control region. The number of OFDM symbols included in thecontrol region of the subframe can be known by using the PCFICH.

The control region consists of a plurality of control channel elements(CCEs) that is a logical CCE stream. Hereinafter, the CCE stream denotesa set of all CCEs constituting the control region in one subframe. TheCCE corresponds to a plurality of resource element groups. For example,the CCE may correspond to 9 resource element groups. The resourceelement group is used to define mapping of a control channel onto aresource element. For example, one resource element group may consist offour resource elements.

A plurality of PDCCHs may be transmitted in the control region. ThePDCCH carries control information such as scheduling allocation. ThePDCCH is transmitted on an aggregation of one or several consecutiveCCEs. A PDCCH format and the number of available PDCCH bits aredetermined according to the number of CCEs constituting the CCEaggregation. Hereinafter, the number of CCEs used for PDCCH transmissionis referred to as a CCE aggregation level. The CCE aggregation level isa CCE unit for searching for the PDCCH. A size of the CCE aggregationlevel is defined by the number of contiguous CCEs. For example, the CCEaggregation level may be an element of {1, 2, 4, 8}.

Table 1 below shows an example of the PDCCH format and the number ofavailable PDCCH bits with respect to the CCE aggregation level.

TABLE 1 PDCCH CCE aggregation Number of resource Number of format levelelement group PDCCH bits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

Control information transmitted through the PDCCH is referred to asdownlink control information (hereinafter, DCI). The DCI includes uplinkscheduling information, downlink scheduling information, systeminformation, an uplink power control command, control information forpaging, control information for indicating a random access channel(RACH) response, etc.

Examples of the DCI format include a format 0 for scheduling of aphysical uplink shared channel (PUSCH), a format 1 for scheduling of onephysical downlink shared channel (PDSCH) codeword, a format 1A forcompact scheduling of the one PDSCH codeword, a format 1B for simplescheduling for rank-1 transmission of a single codeword in a spatialmultiplexing mode, a format 1C for significantly compact scheduling of adownlink shared channel (DL-SCH), a format 1D for scheduling of thePDSCH in a multi-user spatial multiplexing mode, a format 2 forscheduling of the PDSCH in a closed-loop spatial multiplexing mode, aformat 2A for scheduling of the PDSCH in an open-loop spatialmultiplexing mode, a format 3 for transmission of a transmission powercontrol (TPC) command for 2-bit power control for the PUCCH and thePUSCH, and a format 3A for transmission of a TPC command for 1-bit powercontrol for the PUCCH and the PUSCH.

FIG. 11 is a flowchart showing a method of configuring a PDCCH.

Referring to FIG. 11, information bits of control information arearranged to constitute a plurality of information fields. The pluralityof information fields are multiplexed according to an order of a DCIformat list. A BS may select one DCI format from a plurality of DCIformats according to the control information to be transmitted.

A cyclic redundancy check (CRC) for error detection is attached to thecontrol information conforming to the DCI format (step S110). Anidentifier (i.e., a radio network temporary identifier (RNTI)) is maskedto the CRC according to a usage or owner of the PDCCH. Examples of theRNTI include a cell (C)-RNTI that is a unique identifier, a temporaryC-RNTI that is a temporary identifier of a UE and is used in a randomaccess process, a paging (P)-RNTI that is an identifier for a pagingmessage transmitted through a PCH, a system information (SI)-RNTI forsystem information transmitted through a DL-SCH, a random access(RA)-RNTI for a random access response to a random access preamble ofthe UE, etc.

Channel coding is performed on the CRC-attached control information togenerate coded data (step S120). A rate matching is performed on thecoded data according to a CCE aggregation level assigned to the PDCCHformat (step S130). The coded data is modulated to generate modulationsymbols. The CCE aggregation level of modulation symbols constitutingone PDCCH may be one of 1, 2, 4, and 8. The modulation symbols aremapped to physical resource elements.

FIG. 12 shows a method of transmitting control information according toan embodiment of the present invention.

Referring to FIG. 12, a BS transmits downlink control information (DCI)through a PDCCH (step S210). The BS selects a DCI format and transmitsthe DCI according to the selected DCI format. It is assumed herein thatthe DCI format 1B is used for simple scheduling for rank-1 transmissionof a single codeword in a spatial multiplexing mode.

Table 2 shows an example of the DCI transmitted using the DCI format 1B.

TABLE 2 Information field bit(s) Localized/Distributed VRB assignmentflag 1 Resource block assignment [log₂(N_(RB) ^(DL)(N_(RB) ^(DL) +1)/2)] Modulation and coding scheme 5 HARQ process number 3(FDD), 4(TDD)New data indicator 1 Redundancy version 2 TPC command for PUCCH 2Downlink Assignment Index 2 TPMI information for precoding 2 or 4 PMIconfirmation for precoding 1

The DCI format 1B includes a plurality of information fields. Theplurality of information fields include a localized/distributed virtualresource block (VRB) assignment flag field, a resource block assignmentfield, a modulation and coding scheme (MCS) field, an HARQ processnumber field, a new data indicator field, a redundancy version field, aTPC command field for PUCCH, a downlink assignment index field, atransmitted preceding matrix indicator (TPMI) information field forpreceding, a PMI confirmation field for preceding, etc. The number ofbits of each information field is for exemplary purposes only, and thusthe size of information field is not limited thereto.

The localized/distributed VRB assignment flag field is an informationfield for identifying localized VRB assignment in which resource blocksare consecutively assigned or distributed VRB assignment in whichresource blocks are distributively assigned.

The resource block assignment field may have a different bit sizeaccording to the localized VRB or the distributed VRB. For the localizedVRB, ┌ log₂(N_(RB) ^(DL)(N_(RB) ^(DL)+1)/2)┐ bits are provided to theresource assignment. Herein, N_(RB) ^(DL) denotes the number of resourceblocks included in a downlink slot, and depends on a downlink transmitbandwidth determined in a cell. For the distributed VRB, ┌ log₂(N_(RB)^(DL)(N_(RB) ^(DL)+1)/2)┐ bits are provided to the resource assignmentif N_(RB) ^(DL) is less than 50, and ┌ log₂(N_(RB) ^(DL)(N_(RB)^(DL)+1)/2)┐−1 bits are provided to the resource assignment if N_(RB)^(DL) is greater than or equal to 50.

The TPMI information field indicates a codebook index corresponding to asingle layer, i.e., a rank-1 transmission. Table 3 shows an example ofthe number of bits of the TPMI information field with respect to thenumber of antenna ports.

TABLE 3 Number of antenna Number of bits for ports at eNode-B TPMIinformation 2 2 4 4

When the number of antenna ports is 2, the TPMI information field uses 2bits. When the number of antenna ports is 4, the TPMI information fielduses 4 bits. The number of antenna ports is shown for exemplary purposesonly. Thus, the number of antenna ports may vary such as 6, 8, and soone, and the number of bits of the TPMI information field may also varyaccording to the number of antenna ports.

Table 4 shows an example of a codebook index indicated by the TPMIinformation field for two antenna ports.

TABLE 4 Bit field mapped to index Message 0 PMI = 0 1 PMI = 1 2 PMI = 23 PMI = 3

Table 4 shows an example of a codebook index indicated by the TPMIinformation field for four antenna ports.

TABLE 5 Bit field mapped to index Message 0 PMI = 0 1 PMI = 1 . . . . .. 15  PMI = 15

The PMI confirmation field indicates whether preceding for downlink datatransmission will be performed using a PMI indicated by the TPMIinformation field or whether preceding for downlink data transmissionwill be performed using a last PMI reported through a PUSCH. That is,the TPMI information field indicates whether preceding for downlink datatransmission will be performed using a PMI reported by a UE. Table 6shows an example of content indicated by the PMI confirmation field.

TABLE 6 Bit field mapped to index Message 0 Precoding according to theindicated TPMI in the TPMI information field 1 Precoding according tothe latest PMI report on PUSCH using the precoder(s) indicated by thereported PMI(s)

A PMI confirmation message is a message indicating that preceding isperformed using the last PMI reported through the PUSCH indicated by abit value ‘1’ of the PMI confirmation field. The PMI confirmationmessage implies that preceding is performed according to the PMIreported by the UE.

The PMI reported by the UE varies according to single user (SU)-MIMOusing spatial multiplexing for a single user or multi user (MU)-MIMOusing spatial multiplexing for multiple users. In the SU-MIMO, the UEmay select a specific frequency band from a wideband and transmit a PMIfor the selected frequency band. The PMI for the selected frequency bandis referred to as a frequency selective PMI. In the MU-MIMO, the UEtransmits only a PMI for the wideband. The PMI for the wideband isreferred to as a frequency flat PMI. The frequency flat PMI may beaperiodically transmitted through the PUSCH or may be periodicallytransmitted through the PUCCH. The MU-MIMO is used under the conditionof a high correlated antenna configuration. Thus, the PMI confirmationfield is unnecessary information when using the MU-MIMO.

Hereinafter, a method of effectively configuring the information fieldof the DCI by using the PMI confirmation filed when using the MU-MIMOwill be described.

(1) 1^(st) Embodiment

The PMI confirmation field included in the DCI conforming to the DCIformat 1B can be used as a downlink power offset field. Therefore, theDCI using the DCI format 1B can be configured as shown in Table 7.

TABLE 7 Information field bit(s) Localized/Distributed VRB assignmentflag 1 Resource block assignment [log₂(N_(RB) ^(DL)(N_(RB) ^(DL) +1)/2)] Modulation and coding scheme 5 HARQ process number 3(FDD), 4(TDD)New data indicator 1 Redundancy version 2 TPC command for PUCCH 2Downlink Assignment Index 2 TPMI information for precoding 2 or 4 PMIconfirmation for precoding 0 Downlink power offset 1

The downlink power offset field indicates an offset value of power forrank-1 transmission using a PDSCH in MU-MIMO transmission. A UE mayreceive DCI for each MU-MIMO transmission and thus differently analyzethe DCI.

Table 8 shows an example of the number of bits of the TPMI informationfield and the number of bits of the downlink power offset with respectto the number of antenna ports.

TABLE 8 Number of antenna Number of bits for Number of bits for ports ateNode-B TPMI information downlink power offset 2 2 1 4 4 1

The number of bits of the downlink power offset can be used to indicatea power offset value by using one bit both for 2 antenna ports and 4antenna ports. Power information is transmitted through upper-layersignaling. Values of 0 dB and −3 dB against a power value used by asingle user can be used as the power offset value. Table 9 shows anexample of a power offset value with respect to a bit value of a 1-bitdownlink power offset field.

TABLE 9 Downlink power offset field Power offset (dB) 0 −10log₁₀2 1 0

(2) 2^(nd) Embodiment

In 4Tx transmission, that is, in transmission using 4 antenna ports, a3-bit codebook consisting of a subset of a 4-bit codebook can bedefined, and thus the TPMI information field can be used in 3 bits. Thatis, the TPMI information field can indicate a codebook of a subsetconsisting of a part of a codebook used in downlink data transmission.The remaining one bit of the TPMI information field and the PMIconfirmation field may be used as the downlink power offset field.Therefore, the DCI using the DCI format 1B in the MU-MIMO can beconfigured as shown in Table 10.

TABLE 10 Information field bit(s) Localized/Distributed VRB assignmentflag 1 Resource block assignment [log₂(N_(RB) ^(DL)(N_(RB) ^(DL) +1)/2)] Modulation and coding scheme 5 HARQ process number 3(FDD), 4(TDD)New data indicator 1 Redundancy version 2 TPC command for PUCCH 2Downlink Assignment Index 2 TPMI information for precoding 2 or 3 PMIconfirmation for precoding 0 Downlink power offset 2

Table 11 shows another example of the number of bits of the TPMIinformation field and the number of bits of the downlink power offsetwith respect to the number of antenna ports.

TABLE 11 Number of antenna Number of bits for Number of bits for portsat eNode-B TPMI information downlink power offset 2 2 1 4 3 2

Power information is transmitted through upper-layer signaling. Valuesof 0 dB, −3 dB, −10 log₁₀(⅓), and −6 dB against a power value used by asingle user can be used as the power offset value. Table 12 shows anexample of a power offset value with respect to a bit value of a 2-bitdownlink power offset field.

TABLE 12 Downlink power offset field Power offset (dB) 00 0 01 −3 10−10log₁₀ (⅓) 11 −6

The power offset with respect to the number of bits of the downlinkpower offset field shown in Table 9 and Table 12 is shown for exemplarypurposes only. Thus, various power offset values can be defineddepending on a system.

(3) 3^(rd) Embodiment

In 4Tx transmission, the localized/distributed VRB assignment flag fieldand the PMI confirmation field can be used as the downlink power offsetfield. Therefore, the DCI using the DCI format 1B in the MU-MIMO can beconfigured as shown in Table 13.

TABLE 13 Information field bit(s) Localized/Distributed VRB assignmentflag 0 Resource block assignment [log₂(N_(RB) ^(DL)(N_(RB) ^(DL) +1)/2)] Modulation and coding scheme 5 HARQ process number 3(FDD), 4(TDD)New data indicator 1 Redundancy version 2 TPC command for PUCCH 2Downlink Assignment Index 2 TPMI information for precoding 2 or 4 PMIconfirmation for precoding 0 Downlink power offset 2

Table 14 shows another example of the number of bits of the TPMIinformation field and the number of bits of the downlink power offsetwith respect to the number of antenna ports.

TABLE 14 Number of antenna Number of bits for Number of bits for portsat eNode-B TPMI information downlink power offset 2 2 2 4 4 2

The power offset value with respect to the number of bits of the 2-bitdownlink power offset field can be expressed by Table 12. Thelocalized/distributed VRB assignment flag field and the PMI confirmationfield can also be used in 2Tx transmission as the 2-bit downlink poweroffset field.

(4) 4^(th) Embodiment

In 4Tx transmission, a 3-bit codebook consisting of a subset of a 4-bitcodebook can be defined, and thus the TPMI information field can be usedin 3 bits. The remaining one bit of the TPMI information field and thePMI confirmation field can be used as the 1-bit interference vectorfield and the 1-bit downlink power offset field. The interference vectorfield indicates interference information of downlink transmission oruplink transmission. For example, a signal to interference ratio (SINR)value or a difference value thereof may be indicated according to a bitvalue of the interference vector field. Therefore, the DCI using the DCIformat 1B in the MU-MIMO can be configured as shown in Table 15.

TABLE 15 Information field bit(s) Localized/Distributed VRB assignmentflag 1 Resource block assignment [log₂(N_(RB) ^(DL)(N_(RB) ^(DL) +1)/2)] Modulation and coding scheme 5 HARQ process number 3(FDD), 4(TDD)New data indicator 1 Redundancy version 2 TPC command for PUCCH 2Downlink Assignment Index 2 TPMI information for precoding 2 or 3 PMIconfirmation for precoding 0 Downlink power offset 1 Interference vector1

Table 16 shows another example of the number of bits of the TPMIinformation field, the number of bits of the downlink power offset, andthe number of bits of the interference vector field with respect to thenumber of antenna ports.

TABLE 16 Number of bits Number of antenna Number of bits for fordownlink Interference ports at eNode-B TPMI information power offsetvector 2 2 1 0 0 1 4 3 1 1

In 2Tx transmission, the PMI confirmation field can be used as thedownlink power offset field or the interference vector field. An orderof using fields from the TPMI information field and the PMI confirmationfield to the downlink power offset field and the interference vectorfield may be a forward or backward order.

(5) 5^(th) Embodiment

In 4Tx transmission, a 3-bit codebook consisting of a subset of a 4-bitcodebook can be defined, and thus the TPMI information field can be usedin 3 bits. The remaining one bit of the TPMI information field and thePMI confirmation field can be used as a 2-bit interference vector field.Therefore, the DCI using the DCI format 1B in the MU-MIMO can beconfigured as shown in Table 17.

TABLE 17 Information field bit(s) Localized/Distributed VRB assignmentflag 1 Resource block assignment [log₂(N_(RB) ^(DL)(N_(RB) ^(DL) +1)/2)] Modulation and coding scheme 5 HARQ process number 3(FDD), 4(TDD)New data indicator 1 Redundancy version 2 TPC command for PUCCH 2Downlink Assignment Index 2 TPMI information for precoding 2 or 3 PMIconfirmation for precoding 0 Interference vector 2

Table 18 shows another example of the number of bits of the TPMIinformation field and the number of bits of the interference vectorfield with respect to the number of antenna ports.

TABLE 18 Number of antenna Number of bits for Interference ports ateNode-B TPMI information vector 2 2 1 4 3 2

In 2Tx transmission, the PMI confirmation field can be used as a 1-bitinterference vector field.

(6) 6^(th) Embodiment

In 4Tx transmission, the localized/distributed VRB assignment flag fieldand the PMI confirmation field can be used as the 1-bit interferencevector field and the 1-bit downlink power offset field. Therefore, theDCI using the DCI format 1B in the MU-MIMO can be configured as shown inTable 19.

TABLE 19 Information field bit(s) Localized/Distributed VRB assignmentflag 0 Resource block assignment [log₂(N_(RB) ^(DL)(N_(RB) ^(DL) +1)/2)] Modulation and coding scheme 5 HARQ process number 3(FDD), 4(TDD)New data indicator 1 Redundancy version 2 TPC command for PUCCH 2Downlink Assignment Index 2 TPMI information for precoding 2 or 4 PMIconfirmation for precoding 0 Downlink power offset 1 Interference vector1

Table 20 shows another example of the number of bits of the TPMIinformation field, the number of bits of the downlink power offset, andthe number of bits of the interference vector field with respect to thenumber of antenna ports.

TABLE 20 Number of bits Number of antenna Number of bits for fordownlink Interference ports at eNode-B TPMI information power offsetvector 2 2 1 1 4 4 1 1

In 2Tx transmission, the localized/distributed VRB assignment flag fieldand the PMI confirmation field can also be used as the downlink poweroffset field and the interference vector field. An order of using fieldsfrom the localized/distributed VRB assignment flag field and the PMIconfirmation field to the downlink power offset field and theinterference vector field may be a forward or backward order.

(7) 7^(th) Embodiment

In 4Tx transmission, the localized/distributed VRB assignment flag fieldand the PMI confirmation field can be used as the 2-bit interferencevector field. Therefore, the DCI using the DCI format 1B in the MU-MIMOcan be configured as shown in Table 21.

TABLE 21 Information field bit(s) Localized/Distributed VRB assignmentflag 0 Resource block assignment [log₂(N_(RB) ^(DL)(N_(RB) ^(DL) +1)/2)] Modulation and coding scheme 5 HARQ process number 3(FDD), 4(TDD)New data indicator 1 Redundancy version 2 TPC command for PUCCH 2Downlink Assignment Index 2 TPMI information for precoding 2 or 4 PMIconfirmation for precoding 0 Interference vector 2

Table 22 shows another example of the number of bits of the TPMIinformation field and the number of bits of the interference vectorfield with respect to the number of antenna ports.

TABLE 22 Number of antenna Number of bits for Interference ports ateNode-B TPMI information vector 2 2 2 4 4 2

In 2Tx transmission, the localized/distributed VRB assignment flag fieldand the PMI confirmation field can be used as the 2-bit interferencevector field.

(8) 8^(th) Embodiment

In 2Tx transmission, a 2-bit codebook consisting of a subset of a 4-bitcodebook can be defined. In 2Tx transmission, the localized/distributedVRB assignment flag field and the PMI confirmation field can be used asthe 2-bit interference vector field. The DCI using the DCI format 1B inthe MU-MIMO can be configured as shown in Table 21. The number of bitsof the TPMI information field and the number of bits of the interferencevector field with respect to the number of antenna ports can bedescribed as shown in Table 22.

(9) 9^(th) Embodiment

In 2Tx transmission, the localized/distributed VRB assignment flag fieldand the PMI confirmation field can be used as the 2-bit downlink poweroffset field. The DCI using the DCI format 1B in the MU-MIMO can beconfigured as shown in Table 13. The number of bits of the TPMIinformation field and the number of bits of the downlink power offsetfield with respect to the number of antenna ports can be described asshown in Table 14.

(10) 10^(th) Embodiment

In 2Tx transmission, the localized/distributed VRB assignment flag fieldand the PMI confirmation field can be used as the 1-bit interferencevector field and the 1-bit downlink power offset field. The DCI usingthe DCI format 1B in the MU-MIMO can be configured as shown in Table 19.The number of bits of the TPMI information field, the number of bits ofthe downlink power offset field, and the number of bits of theinterference vector field with respect to the number of antenna portscan be described as shown in Table 20. An order of using fields from thelocalized/distributed VRB assignment flag field and the PMI confirmationfield to the downlink power offset field and the interference vectorfield may be a forward or backward order.

The UE receives downlink data through the PDSCH according to thereceived DCI (step S220). The UE can obtain power information orinterference information from the downlink power offset field or theinterference vector field included in the DCI, and thus can moreeffectively receive the downlink data in the MU-MIMO.

Power information or interference information can be obtained from aninterference vector field or a downlink power offset field included indownlink control information (DCI), and downlink data can be moreeffectively transmitted using multi user (MU)-multiple input multipleoutput (MIMO).

Every function as described above may be performed by processors such asa microprocessor, a controller, a microcontroller, an ASIC (ApplicationSpecific Integrated Circuit), and the like, based on software coded toperform such functions or program codes. Designing, developing, andimplementing the codes may be obvious to the person in the art based onthe description of the present invention.

The preferred embodiments of the present invention have been describedwith reference to the accompanying drawings, and it will be apparent tothose skilled in the art that various modifications and variations canbe made in the present invention without departing from the scope of theinvention. Thus, it is intended that any future modifications of theembodiments of the present invention will come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of transmitting control information in awireless communication system, the method comprising: configuring, by abase station, downlink control information (DCI) comprising a pluralityof information fields, wherein the plurality of information fieldscomprise a transmitted precoding matrix indicator (TPMI) informationfield for indicating a codebook index, a downlink power offset of powerfor downlink data transmission, and a virtual resource block (VRB)assignment flag field for identifying whether a resource block isassigned in a consecutive manner or a distributed manner, wherein thedownlink power offset of power for downlink data transmission is 1bitinformation, which is set to a first offset value indicating ‘0 (dB)’ ora second offset value indicating ‘−10log₁₀2 (dB)’, wherein the downlinkpower offset replaces a precoding matrix indicator (PMI) confirmationfield for indicating whether precoding is performed on downlink data byusing a PMI reported by a user equipment; and transmitting, by the basestation, the downlink control information.
 2. The method of claim 1,wherein the TPMI information field indicates a codebook of a subsetconsisting of a part of a codebook used in the downlink datatransmission.
 3. The method of claim 1, wherein the downlink controlinformation is transmitted through a physical downlink control channel(PDCCH).
 4. The method of claim 1, wherein the transmitted precodingmatrix indicator (TPMI) information field is immediately followed by theinformation field for the downlink power offset.
 5. A transmitter in awireless communication system, the transmitter comprising: a processorconfigured to: configure downlink control information (DCI) comprising aplurality of information fields, wherein the plurality of informationfields comprise a transmitted precoding matrix indicator (TPMI)information field for indicating a codebook index, a downlink poweroffset of power for downlink data transmission, and a virtual resourceblock (VRB) assignment flag field for identifying whether a resourceblock is assigned in a consecutive manner or a distributed manner,wherein the downlink power offset of power for downlink datatransmission is 1bit information, which is set to a first offset valueindicating ‘0 (dB)’ or a second offset value indicating ‘−10log₁₀2(dB)’, wherein the downlink power offset replaces a precoding matrixindicator (PMI) confirmation field for indicating whether precoding isperformed on downlink data by using a PMI reported by a user equipment;and a radio frequency unit coupled to the processor and configured totransmit the DCI to a receiver in the wireless communication system. 6.A receiver in a wireless communication system, the receiver comprising:a radio frequency unit configured to receive downlink controlinformation (DCI) comprising a plurality of information fields, whereinthe plurality of information fields comprise a transmitted precodingmatrix indicator (TPMI) information field for indicating a codebookindex, a downlink power offset of power for downlink data transmission,and a virtual resource block (VRB) assignment flag field for identifyingwhether a resource block is assigned in a consecutive manner or adistributed manner, wherein the downlink power offset of power fordownlink data transmission is 1bit information, which is set to a firstoffset value indicating ‘0 (dB)’ or a second offset value indicating‘−10log₁₀2 (dB)’, wherein the downlink power offset replaces a precodingmatrix indicator (PMI) confirmation field for indicating whetherprecoding is performed on downlink data by using a PMI reported by auser equipment; and a processor coupled to the radio frequency unit andconfigured to operate based on the received DCI.